Polymer, polymer composition and organic light-emitting device

ABSTRACT

A composition comprising a polymer and at least one phosphorescent light-emitting dopant wherein: the polymer comprises a polymer backbone and charge transporting groups pendant from the polymer backbone; the polymer backbone is partially conjugated; and the polymer has a triplet energy level of at least 2.4 eV.

SUMMARY OF THE INVENTION

This invention relates to light-emitting polymer compositions, in particular for use in organic light-emitting devices, and methods of making said compositions and devices.

BACKGROUND OF THE INVENTION

Electronic devices comprising active organic materials are attracting increasing attention for use in devices such as organic light emitting diodes, organic photoresponsive devices (in particular organic photovoltaic devices and organic photosensors), organic transistors and memory array devices. Devices comprising organic materials offer benefits such as low weight, low power consumption and flexibility. Moreover, use of soluble organic materials allows use of solution processing in device manufacture, for example inkjet printing or spin-coating.

An organic light-emitting device (OLED) may comprise a substrate carrying an anode, a cathode and an organic light-emitting layer between the anode and cathode comprising a light-emitting material. Further layers may be provided between the anode and the cathode, for example one or more charge-injection or charge-transport layers.

During operation of the device, holes are injected into the device through the anode and electrons are injected through the cathode. Holes in the highest occupied molecular orbital (HOMO) and electrons in the lowest unoccupied molecular orbital (LUMO) of the light-emitting material combine in the light-emitting layer to form an exciton that releases its energy as light.

Suitable light-emitting materials include small molecule, polymeric and dendrimeric materials. Suitable light-emitting polymers for use in the light-emitting layer include poly(arylene vinylenes) such as poly(p-phenylene vinylenes) and polyarylenes such as polyfluorenes.

The light emitting layer may contain a semiconducting host material and a light-emitting dopant wherein energy is transferred from the host material to the light-emitting dopant.

For example, J. Appl. Phys. 65, 3610, 1989 discloses a host material doped with a fluorescent light-emitting dopant (that is, a light-emitting material in which light is emitted via decay of a singlet exciton) and Appl. Phys. Lett., 2000, 77, 904 discloses a host material doped with a phosphorescent light emitting dopant (that is, a light-emitting material in which light is emitted via decay of a triplet exciton).

Hosts for luminescent dopants include “small molecule” materials such as tris-(8-hydroxyquinoline) aluminium (“Alq3”) and non-conjugated polymers such as polyvinylcarbazole (“PVK”).

Conjugated polymers (that is, polymers in which adjacent repeat units in the polymer backbone are conjugated together) may also be used as host materials. Such conjugated polymers may possess numerous advantageous properties such as solubility, which allows the material to be deposited by solution coating or printing techniques, including processes such as spin-coating or inkjet printing, and high conductivity.

In order to function effectively as a host it is necessary for the relevant excited state energy level of the host material to be higher than that of the luminescent dopant that the host is to be used with (for example, the singlet excited state energy level S₁ for a fluorescent emitter and the triplet excited state energy level T₁ for a phosphorescent emitter). However, conjugation between adjacent repeat units of a conjugated polymer has the effect of lowering the excited state energy levels of the polymer as compared to the excited state energy levels of the monomers from which those repeat units are derived.

WO 2005/013386 discloses an organic light-emitting device comprising a host polymer material and a luminescent metal complex wherein the polymer material may comprise non-planar repeat units or partially or fully non-conjugated repeat units in order to reduce conjugation of the polymer.

WO 2008/143387 discloses a polymer that may be used as a host material wherein the polymer has side-chains containing Si or Sn atoms.

WO 2009/080799 discloses Carbazole group-containing ROMP-prepared norbornene derivative polymers.

WO 2006/137434 discloses a polyfluorene comprising hole transporting functional side-groups.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a composition comprising a polymer and at least one phosphorescent light-emitting dopant wherein:

the polymer comprises a polymer backbone and charge transporting groups pendant from the polymer backbone; the polymer backbone is partially conjugated; and the polymer has a triplet energy level of at least 2.4 eV.

Optionally, the polymer backbone comprises one or more highly conjugating repeat units and one or more conjugation-reducing repeat units that increase the triplet energy level of the polymer as compared to a polymer containing the highly conjugating repeat units only.

Optionally, a triplet excited state energy level of the polymer is at least 0.1 eV higher, optionally at least 0.3 eV higher, than a corresponding triplet excited state energy level of the polymer containing the highly conjugating repeat units only.

Optionally, the one or more conjugation-reducing repeat units are selected from:

non-conjugating repeat units that break any conjugation path between repeat units adjacent to the non-conjugating repeat unit; and conjugation-limited repeat units having a substitution pattern and/or linkage to adjacent repeat units that limits the extent of conjugation of the repeat unit to adjacent repeat units.

Optionally, one or more highly conjugating repeat units are not substituted at any position adjacent to linking positions linking the highly conjugating repeat unit to adjacent repeat units.

Optionally, the polymer comprises at least one conjugation-limited repeat unit, and wherein the conjugation-limited repeat unit has at least one substituent at a position adjacent to at least one position linking the conjugation-limited repeat unit to adjacent repeat units.

Optionally, the polymer comprises repeat units of formula (I):

wherein Ar⁶ independently in each occurrence represents an aryl or heteroaryl group that is unsubstituted or substituted with one or more substituents R¹, and w is at least 1, optionally 1, 2 or 3.

Optionally, Ar⁶ is substituted with one or more substituents R¹ independently selected in each occurrence from the group consisting of optionally substituted alkyl, optionally C₁₋₂₀ alkyl, wherein one or more non-adjacent C atoms may be replaced with O, S, substituted N, C═O and —COO—; optionally substituted aryl or heteroaryl, in particular aryl or heteroaryl substituted with one or more alkyl groups, optionally C₁₋₂₀ alkyl; and optionally substituted arylalkyl or heteroarylalkyl.

Optionally, the polymer comprises spacer groups spacing the charge transporting groups from the polymer backbone.

Optionally, at least one substituent R¹ has formula formula -(Sp)_(n)-CT, wherein Ar in each occurrence independently represents an optionally substituted aryl or heteroaryl group; n is 0 or 1; Sp in each occurrence independently in each occurrence represents a spacer group; and CT represents the charge transporting group.

Optionally, Sp comprises at least one atom between CT and Ar⁶ breaking any conjugation path between CT and Ar⁶.

Optionally, Sp is an alkyl chain, optionally a C₁₋₂₀ alkyl chain, wherein one or more H atoms of the alkyl chain may be replaced with F, and one or more non-adjacent C atoms may be replaced with: a substituted or unsubstituted aromatic or heteroaromatic group; O; S; COO; or substituted N.

Optionally, Ar⁶ represents an optionally substituted monocyclic or polycyclic aromatic group.

Optionally, the polymer comprises at least one highly conjugating repeat unit of formula (I) and at least one conjugation-limited repeat unit of formula (I).

Optionally, the highly conjugating repeat unit of formula (I) is a 2,7-linked fluorene repeat unit of formula (IVa):

wherein R² in each occurrence is H or a substituent R¹ as described above, and the repeat unit of formula (IVa) is not substituted in a position ortho- to its 2- or 7-positions.

Optionally, at least one position of the conjugation-limited repeat unit of formula (I) adjacent to a linking position of the conjugation-limited repeat unit is substituted.

Optionally, the conjugation-limited repeat unit of formula (I) is a phenylene repeat unit of formula (Va):

wherein R¹ is a substituent as described above; and p is at least 1.

Optionally, the charge-transporting group is a hole transporting group.

Optionally, the charge transporting group has formula (VII):

wherein Ar¹ and Ar² in each occurrence are independently selected from optionally substituted aryl or heteroaryl groups, m is greater than or equal to 1, preferably 1 or 2, R is H or a substituent, R8 is H or a substituent, optionally H or C₁₋₂₀ alkyl, and x and y are each independently 1, 2 or 3, and any of Ar¹, Ar² and R may be linked by a direct bond or a divalent linking group.

Optionally, the charge-transporting group is an electron-transporting group.

Optionally, the charge-transporting group has formula (VIII):

wherein Ar¹, Ar² and Ar^(a) in each occurrence are independently selected from optionally substituted aryl or heteroaryl groups, and z is at least 1, optionally 1, 2 or 3.

Optionally, the polymer and the at least one light-emitting dopant are blended together.

Optionally, the at least one light-emitting dopant is bound to the polymer.

Optionally, the at least one light-emitting dopant is a blue light-emitting dopant.

Optionally, the at least one light-emitting dopant is a green light-emitting dopant.

In a second aspect, the invention provides a formulation comprising the composition according to the first aspect and at least one solvent.

Optionally according to the second aspect, the at least one solvent is selected from benzene substituted with one or more alkyl or alkoxy groups.

In a third aspect, the invention provides an organic light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and the cathode wherein the light-emitting layer comprises a composition according to the first aspect.

In a fourth aspect, the invention provides a method of forming a light-emitting device according to the third aspect, the method comprising the steps of depositing the light-emitting layer over one of the anode and the cathode and depositing the other of the anode and the cathode over the light-emitting layer.

Optionally according to the fourth aspect, the light-emitting layer is formed by depositing a formulation according to the second aspect and evaporating the at least one solvent.

In a fifth aspect the invention provides a polymer comprising a repeat unit of formula (Vd), (Ve) or (Vf):

wherein R¹ in each occurrence is the same or different and represents a substituent; p is at least 1; and at least one group R¹ has formula -(Sp)_(n)-CT, wherein n is 0 or 1; Sp in each occurrence independently in each occurrence represents a spacer group; and CT represents a charge transporting group.

R¹, Sp, CT, p and n of the fifth aspect may be as described anywhere herein. Polymers of the fifth aspect may be copolymers comprising a repeat unit of formula (Vd), (Ve) or (Vf) and one or more co-repeat units other repeat unit of formula (Vd), (Ve) or (Vf). Co-repeat units may be as described anywhere herein, for example fluorene or phenylene repeat units.

Optionally according to the fifth aspect, p is 1 or 2.

Optionally according to the fifth aspect, p is at least 2 and at least one group R¹ has formula -(Sp)_(n)-CT.

A polymer of the fifth aspect may be formed by polymerizing monomers substituted with leaving groups as described anywhere herein, for example halogen, boronic acid or boronic ester leaving groups, to form a polymer comprising a repeat unit of formula (Vd), (Ve) or (Vf).

In a sixth aspect the invention provides a composition comprising a polymer according to the fifth aspect and a phosphorescent light-emitting dopant.

In a seventh aspect the invention provides an organic light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and the cathode wherein the light-emitting layer comprises a composition according to the sixth aspect. Devices of the seventh aspect may have a device structure as described anywhere herein.

“Aryl(ene)” and “heteroaryl(ene)” as used herein includes both fused and unfused aryl and heteroaryl groups respectively.

DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to the drawings in which:

FIG. 1 illustrates an organic light-emitting device according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Polymer Backbone

The backbone of the polymer is formed from the backbone units of repeat units of the polymer linked together to form a chain.

The backbone of the polymer is partially conjugated, and backbone units may be selected from highly conjugating repeat units and repeat units that reduce the extent of conjugation in the polymer backbone as compared to a backbone containing only the conjugating repeat units. Repeat units in the backbone that reduce the extent of conjugation may include one or both of non-conjugating repeat units and limited conjugation repeat units.

The polymer may comprise a repeat unit of formula (I) as described above:

wherein Ar⁶ independently in each occurrence represents an aryl or heteroaryl group that is unsubstituted or substituted with one or more substituents R¹, and w is at least 1, optionally 1, 2 or 3.

The repeat unit of formula (I) may be a highly conjugated repeat unit or a limited conjugation repeat unit depending on the linkage position and/or substitution positions of the repeat unit of formula (I).

Ar⁶ is optionally substituted with one or more substituents R¹. Preferably, each R¹ is independently selected from the group consisting of optionally substituted alkyl, optionally C₁₋₂₀ alkyl, wherein one or more non-adjacent C atoms may be replaced with O; S; NH; substituted N, e.g. alkyl or phenyl substituted N; C═P; —COO—; optionally substituted aryl or heteroaryl, in particular aryl or heteroaryl substituted with one or more alkyl groups, e.g. C₁₋₂₀ alkyl; and optionally substituted arylalkyl or heteroarylalkyl. More preferably, at least one R¹ comprises an optionally substituted alkyl, e.g. C₁-C₂₀ alkyl; optionally substituted aryl, in particular optionally substituted phenyl, for example unsubstituted phenyl or phenyl substituted with one or more C₁₋₂₀ alkyl groups; and a charge-transporting sidechain of formula -(Sp)_(n)-CT. The repeat unit of formula (I) may include one or more substituents R¹ of formula -(Sp)_(n)-CT and one or more substituents R¹ other than -(Sp)_(n)-CT, for example one or more C₁₋₂₀ alkyl groups.

In the case where one or more groups R¹ is a charge-transporting sidechain, the repeat unit of formula (I) may have a formula (IIa) or (IIb) in the case where w is 1 or 2 respectively, or (IIc) or (IId) in the case where w is 3:

wherein v is at least 1, optionally 1 or 2.

Ar⁶ may be a monocyclic or polycyclic aromatic, for example phenylene, fluorene or indenofluorene.

The charge transporting group pendant from the polymer backbone is selected from charge-transporting groups having a triplet-energy level higher than that of the one or more phosphorescent dopants in the composition.

However, the triplet energy level of the polymer backbone decreases as the extent of conjugation in the polymer backbone increases. If the extent of conjugation in the polymer backbone is too high then the triplet energy level of the polymer backbone may be lower than that of the dopant, resulting in quenching of phosphorescence.

The extent of conjugation in the polymer backbone may be controlled by selection of highly conjugating and limited conjugation repeat units so that the triplet energy level of the backbone is at least the same as or higher than the triplet energy level of the phosphorescent dopant or dopants used with the polymer.

A limited conjugation repeat unit may be internally conjugated but linked through linkage positions and/or substituted with substituents that limit the extent to which the repeat unit is capable of conjugating with adjacent repeat units.

The partial conjugation of the backbone may be provided by polymerization of monomers containing aryl, heteroaryl and/or conjugated vinyl groups to form conjugating repeat units that conjugate to aryl, heteroaryl or vinyl groups of an adjacent repeat unit.

Non-conjugating or limited conjugation repeat units may be provided within the polymer backbone to reduce or break conjugation along the backbone, and the ratio of highly conjugating repeat units to limited conjugation and/or non-conjugating repeat units may be selected such that the triplet level of the polymer is at least about 2.4 eV.

A highly conjugating repeat unit may be any repeat unit capable of conjugating with adjacent repeat units so as to provide a conjugation path between the adjacent repeat units, as illustrated by a chain of phenyl repeat units:

The 1,4 linkage of phenyl unit B provides for a conjugation path between adjacent units A and C, and a resonance structure of the 3 units can be drawn. Units A and C are fully conjugated. Accordingly, a highly conjugating repeat unit may be a repeat unit for which a resonance structure exists for the group of the highly conjugating repeat unit and its adjacent repeat units.

The conjugation of a repeat unit may be limited by changing its linkage position to adjacent repeat units, as illustrated by the following chain of phenylene repeat units:

Linkage through the 1,3-positions means that there is no path of alternating double and single bonds between units A and C, and no resonance structure exists for the group of the conjugation-limited repeat unit and its adjacent repeat units. As such, although there may be some conjugation between units A and C, the extent of conjugation is limited.

Alternatively or additionally, a limited conjugation repeat unit may be a repeat unit that is twisted out of the plane of the polymer backbone, thereby reducing pi orbital overlap between adjacent repeat units, again illustrated below by a chain of phenyl groups:

Twisting of a repeat unit out of plane may be achieved by substituting one or more atoms adjacent (ortho-) to a linking position of the repeat unit with a substituent. Exemplary twisted repeat units may have formula (Ia) or (Ib):

wherein Ar⁶ is an aromatic or heteroaromatic group, preferably an aryl group, more preferably phenyl; R² in each occurrence is H or a substituent R¹ as described above with reference to formula (I), with the proviso that at least one group R², optionally both groups R², is a substituent. Repeat units of formulae (Ia) and (Ib) may be substituted with one or more further substituents R², for example at a position that is not adjacent to a linking position of the repeat unit.

A non-conjugating repeat unit may be any repeat unit that contains one or more non-conjugating atoms, such as one or more sp^(a)-hybridised carbon atoms, that break any conjugation path for conjugation between repeat units on either side of the limited conjugation repeat unit.

Non-conjugating or limited conjugation repeat units may provide at least 1 mol %, optionally 2 mol %, optionally at least 5 mol %, optionally at least 10 mol % of the total number of repeat units.

The extent of conjugation of the partially conjugated backbone is such that the triplet level of the polymer is at least 2.4 eV.

Random polymerization of monomers for highly conjugating and one or both of non-conjugating repeat units and limited conjugation repeat units may provide a backbone containing conjugated chains of conjugating repeat units separated by non-conjugating or limited conjugation repeat units.

Exemplary repeat units for forming highly conjugating and limited conjugation repeat units include optionally substituted monocyclic and polycyclic arylene repeat units as disclosed in for example, Adv. Mater. 2000 12(23) 1737-1750 and include: 1,2-, 1,3- and 1,4-phenylene repeat units as disclosed in J. Appl. Phys. 1996, 79, 934; 2,7-fluorene repeat units as disclosed in EP 0842208; indenofluorene repeat units as disclosed in, for example, Macromolecules 2000, 33(6), 2016-2020; and spirofluorene repeat units as disclosed in, for example EP 0707020. Each of these repeat units is optionally substituted. Examples of substituents include solubilising groups such as C₁₋₂₀ alkyl or alkoxy; electron withdrawing groups such as fluorine, nitro or cyano; and substituents for increasing glass transition temperature (Tg) of the polymer.

One exemplary class of arylene repeat units is optionally substituted 2,7-linked fluorene repeat units, such as repeat units of formula IV:

wherein R² in each occurrence is the same or different and is H or a substituent R¹ as described above, and wherein the two groups R² may be linked to form a ring.

R² may each independently comprise a linear or branched chain of aryl or heteroaryl groups, each of which groups may independently be substituted, for example a group of formula (Ar³)_(r) as described below with reference to formula (VII). Optionally, at least one R² is a charge-transporting sidechain of formula -(Sp)_(n)-CT as described above.

In the case where R² comprises aryl or heteroaryl, preferred optional substituents include alkyl groups wherein one or more non-adjacent C atoms may be replaced with O, S, N, C═O and —COO—.

R² may comprise a crosslinkable-group, for example a group comprising a polymerisable double bond such and a vinyl or acrylate group, or a benzocyclobutane group.

Optional substituents for aromatic carbon atoms of the fluorene unit, i.e. substituents other than substituents R², are preferably selected from the group consisting of alkyl, for example C₁₋₂₀ alkyl, wherein one or more non-adjacent C atoms may be replaced with 0, S, NH or substituted N, C═O and —COO—, optionally substituted aryl, optionally substituted heteroaryl, alkoxy, alkylthio, fluorine, cyano and arylalkyl. Particularly preferred substituents include C₁₋₂₀ alkyl and substituted or unsubstituted aryl, for example phenyl. Optional substituents for the aryl include one or more C₁₋₂₀ alkyl groups.

A highly conjugating repeat unit of formula (IV) may be a 2,7-linked repeat unit of formula (IVa):

Optionally, the repeat unit of formula (IVa) is not substituted in a position adjacent to the 2- or 7-positions.

Exemplary limited conjugation repeat units of formulae (IV) include repeat units that are: (a) linked through the 3- and/or 6-positions to limit the extent of conjugation across the repeat unit, and/or (b) substituted with one or more further substituents R² in or more positions adjacent to the 2- and 7-positions, for example a 2,7-linked fluorene carrying a substituent R² in one or both of the 3- and 6-positions.

Another exemplary class of arylene repeat units is phenylene repeat units, such as 1,4-phenylene repeat units of formula (Va):

wherein p is 0, 1, 2, 3 or 4, optionally 1 or 2, and R¹ independently in each occurrence is a substituent as described above, for example C₁₋₂₀ alkyl.

If p is 0 then the repeat unit of formula (Va) may be a highly conjugating repeat unit. If p is at least 1 then the repeat unit of formula (Va) may be a limited conjugation repeat unit.

Optionally, at least one R¹ group may be -(Sp)_(n)-CT as described above. In one embodiment, the 1,4-substituted repeat unit of formula (Va) is substituted in its 2- and 5-positions.

In one embodiment, p is 2 and each group R¹, which may be the same or different, is -(Sp)_(n)-CT. Such a repeat unit may provide both functions of charge transport and twist. In this case, the only 2,5-substituted phenylene repeat unit of the polymer may be a a repeat unit of formula (Va) in which each group R² is -(Sp)_(n)-CT.

Exemplary repeat units of formula (Va) include the following:

Limited conjugation repeat units include optionally substituted 1,2- or 1,3-phenylene repeat units of formulae (Vb) and (Vc):

wherein R¹ and p are as described above.

Exemplary limited-conjugation repeat units of formulae (Vb) and (Vc) include the following:

Non-conjugating repeat units may have formula:

—Ar⁷-Sp¹-Ar⁷—

wherein each Ar⁷ independently represents an optionally substituted aryl or heteroaryl group, preferably any aryl group, for example phenyl; and Sp¹ represents a spacer group that does not provide any conjugation path between the two groups Ar⁷.

Sp¹ may contain a single non-conjugating atom between the two groups Ar⁷, for example —O—, —S—, —CR² ₂— wherein R² in each occurrence is H or a substituent, optionally C₁₋₂₀ alkyl. Sp¹ may form a ring or chain separating the two groups Ar⁷.

A spacer chain Sp¹ may contain two or more atoms separating the two groups Ar⁷, for example a C₁₋₂₀ alkyl chain wherein one or more non-adjacent C atoms of the chain may be replaced with O or S.

Examples of cyclic non-conjugating spacers are optionally substituted cyclohexane or adamantane repeat units that may have the structures illustrated below:

Exemplary substituents for cyclic conjugation repeat units include substituents R¹ as described above, in particular alkyl.

Exemplary non-conjugating repeat units include the following:

The polymer may comprise one or more repeat units carrying a pendant charge-transporting group, for example a group of formula -(Sp)_(n)-CT, and one or more repeat units that do not carry a pendant charge-transporting group. Optionally, the polymer comprises at least 1 mol % of repeat units, optionally 1-50 mol %, of repeat units carrying a group of formula -(Sp)_(n)-CT, optionally repeat units of formula (I) substituted with one or more group of formula -(Sp)_(n)-CT. Groups of formula -(Sp)_(n)-CT may be pendant from any repeat unit of the polymer backbone, for example one or more of a highly conjugating repeat unit, a limited conjugation repeat unit and a non-conjugating repeat unit.

Methods for preparation of partially conjugated polymers include “metal insertion” polymerisation wherein the metal atom of a metal complex catalyst is inserted between a monomeric unit such as an aryl or heteroaryl group and a leaving group of a monomer. Exemplary metal insertion polymerisation methods are Suzuki polymerisation as described in, for example, WO 00/53656 and Yamamoto polymerisation as described in, for example, T. Yamamoto, “Electrically Conducting And Thermally Stable π-Conjugated Poly(arylene)s Prepared by Organometallic Processes”, Progress in Polymer Science 1993, 17, 1153-1205. In the case of Yamamoto polymerisation, a nickel complex catalyst is used; in the case of Suzuki polymerisation, a palladium complex catalyst is used.

For example, in the synthesis of a linear polymer by Yamamoto polymerisation, a monomer having two reactive halogen groups is used. Similarly, according to the method of Suzuki polymerisation, at least one reactive group is a boron derivative group such as a boronic acid or boronic ester and the other reactive group is a halogen. Preferred halogens are chlorine, bromine and iodine, most preferably bromine.

It will therefore be appreciated that repeat units illustrated throughout this application may be derived from a monomer carrying suitable leaving groups. Likewise, an end group or side group may be bound to the polymer by reaction of a suitable leaving group.

Suzuki polymerisation may be used to prepare regioregular, block and random copolymers. In particular, homopolymers or random copolymers may be prepared when one reactive group is a halogen and the other reactive group is a boron derivative group. Alternatively, block or regioregular, in particular AB, copolymers may be prepared when both reactive groups of a first monomer are boron and both reactive groups of a second monomer are halogen.

As alternatives to halides, other leaving groups capable of participating in metal insertion include groups include tosylate, mesylate and triflate.

Charge Transporting Polymer Sidechain

The polymer backbone carries charge-transporting sidechains of formula (VI):

-(SP)_(n)-CT  (VI)

wherein n, Sp and CT are as described above.

Sp may be an alkyl chain, for example a branched or linear C₁₋₂₀ alkyl chain. One or more H atoms of the alkyl chain may be replaced with F, and one or more non-adjacent C atoms may be replaced with: an optionally substituted aromatic or heteroaromatic group, for example phenyl optionally substituted with one or more C₁₋₁₀ alkyl groups; O; S: COO; or substituted N, for example N substituted with alkyl group, for example C₁₋₁₀ alkyl.

Sp may form a break in conjugation between CT and the polymer backbone.

Exemplary charge-transporting sidechains have formula —(Ar)_(w)-Alk-CT wherein Ar independently in each occurrence is an optionally substituted aryl or heteroaryl group, preferably an optionally substituted phenyl group, w is 0 or an integer and Alk is C₁₋₂₀ alkyl, preferably C₁₋₁₀ alkyl.

Optionally, one or more non-adjacent C atoms of Alk may be replaced with: an optionally substituted aromatic or heteroaromatic group, for example phenyl optionally substituted with one or more C₁₋₁₀ alkyl groups; O; S: COO; or substituted N, for example N substituted with alkyl group, for example C₁₋₁₀ alkyl. Where one or more non-adjacent atoms of Alk are replaced with aryl or heteroaryl, the replaced atom(s) preferably are not C atoms at the end of Alk.

Optional substituents for Ar include one or more substituents R³ as described with reference to formula (VII), preferably one or more C₁₋₂₀ alkyl groups.

Optionally, where w is an integer it is 1, 2 or 3.

Exemplary spacer groups include:

-   -   a branched, linear or cyclic alkyl chain, for example a C₁₋₂₀         alkyl chain, a 1,4-cyclohexyl group or an adamantane group;     -   a phenylalkyl group, for example a phenyl-C₁₋₂₀ alkyl group         wherein the alkyl group is bound to CT and the phenyl group is         bound to the polymer backbone; and     -   an ether or polyether group, for example a group of formula         —(CH₂CH₂O)_(t)— wherein t is at least 1.

In one exemplary arrangement, the polymer sidechain (VI) may be attached to the polymer after formation of the polymer backbone.

In another exemplary arrangement, the monomers used to form the polymer backbone may be substituted with the sidechain (VI).

In addition to the sidechain of formula (VI), the polymer backbone may be substituted with one or more substituents, for example substituents to increase the solubility of the polymer.

In one arrangement, the sidechains of the polymer may be the same. In another arrangement, two or more different sidechains are provided. Different sidechains may differ in respect of one or more of Ar, n, w, Sp and CT.

The charge-transporting polymer sidechain may be linked to any repeat unit in the polymer backbone, including one or more of a highly conjugating repeat unit, a non-conjugating repeat unit and a limited conjugation repeat unit.

The spacer group, where present, may increase solubility of the polymer as compared to a polymer in which the spacer group is absent. Moreover, the spacer may contain non-conjugating atoms to separate the conjugated charge transporting group from, and prevent conjugation with, any unsaturated groups, such as aromatic groups, that may be present in the backbone or another part of the sidechain.

Charge Transporting Groups

The charge transporting group CT may be any charge-transporting group having a triplet energy level of at least 2.4 eV in order that the triplet energy level of the polymer as a whole is at least 2.4 eV.

The charge transporting group may be a hole transporting group, an electron transporting group or a bipolar group capable of transporting both holes and electrons.

A hole transporting group may have a low electron affinity (2 eV or lower) and low ionisation potential (5.8 eV or lower, preferably 5.7 eV or lower, more preferred 5.6 eV or lower). Electron affinities and ionisation potentials may be measured by cyclic voltammetry (CV) wherein the working electrode potential is ramped linearly versus time.

When cyclic voltammetry reaches a set potential the working electrode's potential ramp is inverted. This inversion can happen multiple times during a single experiment. The current at the working electrode is plotted versus the applied voltage to give the cyclic voltammogram trace.

Apparatus to measure HOMO or LUMO energy levels by CV may comprise a cell containing a tert-butyl ammonium perchlorate/or tertbutyl ammonium hexafluorophosphate solution in acetonitrile, a glassy carbon working electrode where the sample is coated as a film, a platinum counter electrode (donor or acceptor of electrons) and a reference glass electrode no leak Ag/AgCl. Ferrocene is added in the cell at the end of the experiment for calculation purposes. (Measurement of the difference of potential between Ag/AgCl/ferrocene and sample/ferrocene).

Method and settings: 3 mm diameter glassy carbon working electrode Ag/AgCl/no leak reference electrode Pt wire auxiliary electrode 0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile LUMO=4.8−ferrocene (peak to peak maximum average)+onset Sample: 1 drop of 5 mg/mL in toluene spun @3000 rpm LUMO (reduction) measurement: A good reversible reduction event is typically observed for thick films measured at 200 mV/s and a switching potential of −2.5V. The reduction events should be measured and compared over 10 cycles, usually measurements are taken on the 3^(rd) cycle. The onset is taken at the intersection of lines of best fit at the steepest part of the reduction event and the baseline.

An exemplary class of hole transporting groups are amine-containing groups, for example amines of formula (VII):

wherein Ar¹ and Ar² in each occurrence are independently selected from optionally substituted aryl or heteroaryl groups, m is greater than or equal to 1, preferably 1 or 2, R is H or a substituent, R⁸ is H or a substituent, optionally H or C₁₋₂₀ alkyl, and x and y are each independently 1, 2 or 3.

The group of formula (VII) may be bound to the polymer backbone (e.g. to Ar⁶) or to a spacer group Sp through Ar¹, Ar² or R.

R is preferably alkyl, for example C₁₋₂₀ alkyl, Ar³, or a branched or linear chain of Ar³ groups, for example —(Ar³)_(r), wherein Ar³ in each occurrence is independently selected from aryl or heteroaryl and r is at least 1, optionally 1, 2 or 3.

Any of Ar¹, Ar² and Ar³ may independently be substituted with one or more substituents. Preferred substituents are selected from the group R³ consisting of:

-   -   alkyl, for example C₁₋₂₀ alkyl, wherein one or more non-adjacent         C atoms may be replaced with O, S, substituted N, C═O and —COO—         and one or more H atoms of the alkyl group may be replaced with         F or aryl or heteroaryl optionally substituted with one or more         groups R⁴,     -   aryl or heteroaryl optionally substituted with one or more         groups R⁴,     -   NR⁵ ₂, OR⁵, SR⁵,     -   fluorine, nitro and cyano, and     -   crosslinkable groups;         wherein each R⁴ is independently alkyl, for example C₁₋₂₀ alkyl,         in which one or more non-adjacent C atoms may be replaced with         0, S, substituted N, C═O and —COO— and one or more H atoms of         the alkyl group may be replaced with F, and each R⁵ is         independently selected from the group consisting of alkyl and         aryl or heteroaryl optionally substituted with one or more alkyl         groups.

R may comprise a crosslinkable-group, for example a group comprising a polymerisable double bond such and a vinyl or acrylate group, or a benzocyclobutane group.

Any of Ar¹, Ar² and Ar³ in the repeat unit of Formula (VII) may be linked by a direct bond or a divalent linking atom or group. Preferred divalent linking atoms and groups include O, S; substituted N; and substituted C.

Where present, substituted N or substituted C of R³, R⁴ or of the divalent linking group may independently in each occurrence be NR⁶ or CR⁶ ₂ respectively wherein R⁶ is alkyl or optionally substituted aryl or heteroaryl. Optional substituents for aryl or heteroaryl groups R⁶ may be selected from R⁴ or R⁵.

In one preferred arrangement, R is Ar³ and each of Ar¹, Ar² and Ar³ are independently and optionally substituted with one or more C₁₋₂₀ alkyl groups.

Particularly preferred units satisfying Formula (VII) include units of Formulae 1-3:

wherein Ar¹ and Ar² are as defined above; and Ar³ is optionally substituted aryl or heteroaryl. Where present, preferred substituents for Ar³ include substituents as described for Ar¹ and Ar², in particular alkyl and alkoxy groups.

Ar¹, Ar² and Ar³ are preferably phenyl, each of which may independently be substituted with one or more substituents as described above, preferably with one or more C₁₋₂₀ alkyl groups.

In another preferred arrangement, aryl or heteroaryl groups of formula (VII) are phenyl, each phenyl group being optionally substituted with one or more alkyl groups.

In another preferred arrangement, Ar¹, Ar² and Ar³ are phenyl, each of which may be substituted with one or more C₁₋₂₀ alkyl groups, and r=1.

In another preferred arrangement, Ar¹ and Ar² are phenyl, each of which may be substituted with one or more C₁₋₂₀ alkyl groups, and R is 3,5-diphenylbenzene wherein each phenyl may be substituted with one or more alkyl groups.

Exemplary groups of formula (VII) include the following:

wherein the dotted bond indicates the point of attachment of the charge-transporting group to a spacer group or to the polymer backbone.

An electron-transporting group may have a high electron affinity (1.8 eV or higher, preferably 2 eV or higher, even more preferred 2.2 eV or higher) and high ionisation potential (5.8 eV or higher) Suitable electron transport groups include groups disclosed in, for example, Shirota and Kageyama, Chem. Rev. 2007, 107, 953-1010.

Triazines form an exemplary class of electron-transporting groups, for example optionally substituted di or tri-(hetero)aryltriazine attached as a side group through one of the (hetero)aryl groups. Other exemplary electron-transporting groups are pyrimidines and pyridines.

Electron-transporting groups may have formula (VIII):

wherein Ar¹, Ar² and Ar³ are as described with reference to repeat units of formula (VII) and z is at least 1, optionally 1, 2 or 3, and Y is N or CR⁷, wherein R⁷ is H or a substituent, preferably H or C₁₋₁₀ alkyl. The group of formula (VIII) may be linked to the polymer backbone, directly or through a spacer group, through any of Ar¹, Ar² and Ar³.

In one preferred embodiment, all 3 groups Y are N.

If all 3 groups Y are CR⁷ then at least one of Ar¹, Ar² and Ar³ is preferably a heteroaromatic group comprising N.

Each of Ar¹, Ar² and Ar³ may independently be substituted with one or more substituents. In one arrangement, Ar¹, Ar² and Ar³ are phenyl in each occurrence. Exemplary substituents include R³ as described above with reference to formula (VII), for example C₁₋₂₀ alkyl or alkoxy.

Exemplary groups of formula (VIII) include the following.

wherein the dotted bond indicates the point of attachment of the charge-transporting group to a spacer group or to the polymer backbone.

Other suitable electron-transporting materials are sulfoxides and phosphine oxides, benzophenones, and boranes.

Polymeric Repeat Units

In one arrangement, all repeat units of the polymer may have a charge transporting sidechain, for example a sidechain of formula (VI).

In other arrangements, the polymer may contain one or more further repeat units that do not contain a charge transporting sidechain. The further repeat units may be selected to modify the properties of the polymer, for example its electronic or physical properties.

The polymer may comprise different charge-transporting repeat units. For example, the polymer may comprise charge-transporting repeat units that differ in one or more of the structure of the backbone unit, the charge transporting unit and the spacer.

In one arrangement, the polymer may contain different charge-transporting groups. The polymer may contain hole-transporting repeat units comprising pendant hole-transporting groups and electron-transporting repeat units comprising pendant electron-transporting groups. The polymer may contain two or more different hole-transporting groups and/or two or more different electron transporting groups. For example, the polymer may contain two or more different hole transporting groups with different HOMO levels to provide stepped hole transport from the anode or any hole injection or hole transport layer into the light-emitting layer containing the polymer. The same may be done with electron transporting groups to provide stepped electron transport.

The polymer may contain charge transporting repeat units in the polymer backbone as well as in a polymer side-chain. For example, the polymer may comprise a hole-transporting repeat unit of formula (VII) and/or an electron-transporting repeat unit of formula (VIII) linked into the polymer backbone through any two of Ar¹, Ar² and Ar³.

The polymer may comprise hole-transporting repeat units and no electron transporting repeat units, electron transporting repeat units and no hole transporting repeat units or both hole- and electron-transporting repeat units.

A partially conjugated polymer may be formed by co-polymerization of two or more different monomers of formula (IIm):

wherein Ar⁶ and w are as described above; and X represents a leaving group capable of participating in a metal-mediated coupling reaction. One of the monomers of formula (Im) may be a monomer for forming a highly conjugating repeat unit as described above, and another of the monomers of formula (Im) may be a monomer for forming a limited conjugation repeat unit as described above.

One, two or more of the different monomers of formula (IIm) may be substituted with one or more charge-transporting sidechains of formula (VI).

Exemplary monomers of formula (IIm) for forming conjugation-limited repeat units of formula (I) include the following:

Exemplary monomers for forming highly conjugating repeat units of formula (II) include the following:

Light-Emitting Dopant

Materials that may be used as phosphorescent light-emitting dopants include metal complexes comprising optionally substituted complexes of formula (X):

ML¹ _(q)L² _(r)L³ _(s)  (X)

wherein M is a metal; each of L¹, L² and L³ is a coordinating group; q is an integer; r and s are each independently 0 or an integer; and the sum of (a. q)+(b. r)+(c.s) is equal to the number of coordination sites available on M, wherein a is the number of coordination sites on L¹, b is the number of coordination sites on L² and c is the number of coordination sites on L³.

Heavy elements M induce strong spin-orbit coupling to allow rapid intersystem crossing and emission from triplet or higher states (phosphorescence). Suitable heavy metals M include

d-block metals, in particular those in rows 2 and 3 i.e. elements 39 to 48 and 72 to 80, in particular ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum and gold. Iridium is particularly preferred.

The d-block metals are particularly suitable for emission from triplet excited states. These metals form organometallic complexes with carbon or nitrogen donors such as porphyrin or bidentate ligands of formula (XI):

wherein Ar⁴ and Ar⁵ may be the same or different and are independently selected from optionally substituted aryl or heteroaryl; X¹ and Y¹ may be the same or different and are independently selected from carbon or nitrogen; and Ar⁴ and Ar⁵ may be fused together. Ligands wherein X¹ is carbon (for example, Ar⁴ is optionally substituted phenyl) and Y¹ is nitrogen are particularly preferred.

Examples of bidentate ligands are illustrated below:

Each of Ar⁴ and Ar^(y) may carry one or more substituents. Two or more of these substituents may be linked to form a ring, for example an aromatic ring.

Exemplary substituents include groups R³ groups R³ as described above with reference to Formula (VIII). Particularly preferred substituents include fluorine or trifluoromethyl which may be used to blue-shift the emission of the complex, for example as disclosed in WO 02/45466, WO 02/44189, US 2002-117662 and US 2002-182441; alkyl or alkoxy groups, for example C₁₋₂₀ alkyl or alkoxy, which may be as disclosed in JP 2002-324679; carbazole which may be used to assist hole transport to the complex when used as an emissive material, for example as disclosed in WO 02/81448; bromine, chlorine or iodine which can serve to functionalise the ligand for attachment of further groups, for example as disclosed in WO 02/68435 and EP 1245659; and dendrons which may be used to obtain or enhance solution processability of the metal complex as disclosed in WO 02/66552.

A light-emitting dendrimer typically comprises a light-emitting core bound to one or more dendrons, wherein each dendron comprises a branching point and two or more dendritic branches. Preferably, the dendron is at least partially conjugated, and at least one of the branching points and dendritic branches comprises an aryl or heteroaryl group, for example a phenyl group. In one arrangement, the branching point group and the branching groups are all phenyl, and each phenyl may independently be substituted with one or more substituents, for example alkyl or alkoxy.

A dendron may have optionally substituted formula (XII)

wherein BP represents a branching point for attachment to a core and G₁ represents first generation branching groups.

The dendron may be a first, second, third or higher generation dendron. G₁ may be substituted with two or more second generation branching groups G₂, and so on, as in optionally substituted formula (XIIa):

wherein u is 0 or 1; v is 0 if u is 0 or may be 0 or 1 if u is 1; BP represents a branching point for attachment to a core and G₁, G₂ and G₃ represent first, second and third generation dendron branching groups.

BP and/or any group G may be substituted with one or more substituents, for example one or more C₁₋₂₀ alkyl or alkoxy groups.

Other ligands suitable for use with d-block elements include diketonates, in particular acetylacetonate (acac); triarylphosphines and pyridine, each of which may be substituted.

The polymer and the light-emitting dopant may be physically mixed. Alternatively, the light-emitting dopant may be chemically bound to the polymer.

This binding may result in more efficient transfer of excitons from the host polymer to the light emitting dopant because it may provide intramolecular exciton transfer pathways unavailable to a corresponding mixed system.

Moreover, binding may be beneficial for processing reasons. For example, if the light emitting dopant has low solubility then binding it to a soluble polymer allows the light emitting dopant to be carried in solution by the charge transporting material, enabling device fabrication using solution processing techniques. Furthermore, binding the light emitting dopant to the polymer may prevent phase separation effects in solution-processed devices that may be detrimental to device performance.

A non-conjugated polymer having a light-emitting dopant bound thereto in a sidechain of the polymer may be formed by polymerizing a monomer used to form repeat units of formula (I) with a monomer comprising reactive groups containing an unsaturated carbon-carbon bond, in particular a carbon-carbon double bond, and a light-emitting dopant.

A partially conjugated polymer may contain the light-emitting dopant bound as a substituent to polymer backbone, incorporated as a repeat unit in the polymer backbone or provided as an end-group of the polymer, for example as disclosed in EP 1245659, WO 02/31896, WO 03/18653 and WO 03/22908.

The light-emitting dopant may emit light of any colour, preferably a colour within the visible spectrum, for example a red, green or blue light-emitting dopant.

A blue light-emitting dopant may have photoluminescent spectrum with a peak wavelength in the range of less than or equal to 480 nm, such as in the range of 400-480 nm

A green light-emitting dopant may have photoluminescent spectrum with a peak wavelength in the range of above 480 nm-560 nm.

A red light-emitting dopant may have photoluminescent spectrum with a peak wavelength in the range of above 560 nm-630 nm.

More than one light-emitting dopant may be used. For example, red, green and blue light-emitting dopants may be used to obtain white light emission. The polymer of the invention may also emit light, in particular blue light, which may be combined with emission from one or more further dopants to achieve white light.

The light-emitting dopant or dopants may be present in an amount of about 0.05 mol % up to about 50 wt %, optionally about 0.1-40 wt %.

Measurement of the Triplet Level

The triplet energy level of a polymer and a light-emitting dopant may be determined from the onset energy of their phosphorescence spectrum.

According to this method, the material is spin-cast onto a spectrosil substrate mounted inside a vacuum chamber and cooled to approximately 10 k. The film is excited using a pulsed source of 355 nm wavelength and 1 ns pulse width. In order to obtain resolved phosphorescent emission from a fluorescent host polymer, the spectrum is detected after a typical delay period of 1-300 ms. Time-gated spectra were recorded using a Princeton Instruments PI-MAX3 Intensified CCD camera coupled to a PI-Acton 2300 spectrograph.

Light-Emitting Diode

FIG. 1 illustrates an exemplary device comprising a substrate 1, an anode 2, a light-emitting layer 3 and a cathode 4. The light-emitting layer 3 contains a composition as described above. If light is emitted through the substrate 1 then the substrate 1 may be formed from a transparent material, for example glass or plastic. If light is emitted through cathode 4 then the substrate may be opaque.

Further layers may be provided between anode 2 and cathode 4, for example charge transporting, charge injecting and/or charge blocking layers. More than one light-emitting layer may be present between the anode and the cathode.

Hole Injection Layers

A conductive hole injection layer, which may be formed from a conductive organic or inorganic material, may be provided between the anode 2 and the light-emitting layer 3 to assist hole injection from the anode into the layer or layers of semiconducting polymer. Examples of doped organic hole injection materials include optionally substituted, doped poly(ethylene dioxythiophene) (PEDT), in particular PEDT doped with a charge-balancing polyacid such as polystyrene sulfonate (PSS) as disclosed in EP 0901176 and EP 0947123, polyacrylic acid or a fluorinated sulfonic acid, for example Nafion®; polyaniline as disclosed in U.S. Pat. No. 5,723,873 and U.S. Pat. No. 5,798,170; and optionally substituted polythiophene or poly(thienothiophene). Examples of conductive inorganic materials include transition metal oxides such as VOx MoOx and RuOx as disclosed in Journal of Physics D: Applied Physics (1996), 29(11), 2750-2753.

Charge Transporting Layers

A hole transporting layer may be provided between the anode and the light-emitting layer. Likewise, an electron transporting layer may be provided between the cathode and the light-emitting layer.

Similarly, an electron blocking layer may be provided between the anode and the light-emitting layer and a hole blocking layer may be provided between the cathode and the light-emitting layer. Transporting and blocking layers may be used in combination. Depending on its HOMO and LUMO levels, a single layer may both transport one of holes and electrons and block the other of holes and electrons.

If present, a hole transporting layer located between anode 2 and light-emitting layer 3 preferably has a HOMO level of less than or equal to 5.5 eV, more preferably around 4.8-5.5 eV. HOMO levels may be measured by cyclic voltammetry, for example.

If present, an electron transporting layer located between light-emitting layer 3 and cathode 4 preferably has a LUMO level of around 3-3.5 eV. For example, a layer of a silicon monoxide or silicon dioxide or other thin dielectric layer having thickness in the range of 0.2-2 nm is provided between light-emitting layer 3 and layer 4.

Charge transporting units may be provided in a polymer main-chain or polymer side-chain.

Cathode

Cathode 4 is selected from materials that have a workfunction allowing injection of electrons into the electroluminescent layer. Other factors influence the selection of the cathode such as the possibility of adverse interactions between the cathode and the materials of the light-emitting layer. The cathode may consist of a single material such as a layer of aluminium. Alternatively, it may comprise a plurality of metals, for example a bilayer of a low workfunction material and a high workfunction material such as calcium and aluminium as disclosed in WO 98/10621; elemental barium as disclosed in WO 98/57381, Appl. Phys. Lett. 2002, 81(4), 634 and WO 02/84759; or a thin layer of metal compound, in particular an oxide or fluoride of an alkali or alkali earth metal, to assist electron injection, for example lithium fluoride as disclosed in WO 00/48258; barium fluoride as disclosed in Appl. Phys. Lett. 2001, 79(5), 2001; and barium oxide. In order to provide efficient injection of electrons into the device, the cathode preferably has a workfunction of less than 3.5 eV, more preferably less than 3.2 eV, most preferably less than 3 eV. Work functions of metals can be found in, for example, Michaelson, J. Appl. Phys. 48(11), 4729, 1977.

The cathode may be opaque or transparent. Transparent cathodes are particularly advantageous for active matrix devices because emission through a transparent anode in such devices is at least partially blocked by drive circuitry located underneath the emissive pixels. A transparent cathode will comprise a layer of an electron injecting material that is sufficiently thin to be transparent. Typically, the lateral conductivity of this layer will be low as a result of its thinness. In this case, the layer of electron injecting material is used in combination with a thicker layer of transparent conducting material such as indium tin oxide.

It will be appreciated that a transparent cathode device need not have a transparent anode (unless, of course, a fully transparent device is desired), and so the transparent anode used for bottom-emitting devices may be replaced or supplemented with a layer of reflective material such as a layer of aluminium. Examples of transparent cathode devices are disclosed in, for example, GB 2348316.

Encapsulation

OLEDs tend to be sensitive to moisture and oxygen. Accordingly, the substrate preferably has good barrier properties for prevention of ingress of moisture and oxygen into the device. The substrate is commonly glass, however alternative substrates may be used, in particular where flexibility of the device is desirable. For example, the substrate may comprise a plastic as in U.S. Pat. No. 6,268,695 which discloses a substrate of alternating plastic and barrier layers or a laminate of thin glass and plastic as disclosed in EP 0949850.

The device is preferably encapsulated with an encapsulant (not shown) to prevent ingress of moisture and oxygen. Suitable encapsulants include a sheet of glass, films having suitable barrier properties such as silicon dioxide, silicon monoxide, silicon nitride or alternating stacks of polymer and dielectric as disclosed in, for example, WO 01/81649 or an airtight container as disclosed in, for example, WO 01/19142. In the case of a transparent cathode device, a transparent encapsulating layer such as silicon monoxide or silicon dioxide may be deposited to micron levels of thickness, although in one preferred embodiment the thickness of such a layer is in the range of 20-300 nm. A getter material for absorption of any atmospheric moisture and/or oxygen that may permeate through the substrate or encapsulant may be disposed between the substrate and the encapsulant.

Solution Processing

Light-emitting layer 3 may be deposited by any process, including vacuum evaporation and deposition from a solution in a solvent. In the case where the light emitting layer comprises a polyarylene, such as a polyfluorene, suitable solvents for solution deposition include mono- or poly-alkylbenzenes such as toluene and xylene. Particularly preferred solution deposition techniques including printing and coating techniques, preferably spin-coating and inkjet printing.

Spin-coating is particularly suitable for devices wherein patterning of the electroluminescent material is unnecessary—for example for lighting applications or simple monochrome segmented displays.

Inkjet printing is particularly suitable for high information content displays, in particular full colour displays. A device may be inkjet printed by providing a patterned layer over the first electrode and defining wells for printing of one colour (in the case of a monochrome device) or multiple colours (in the case of a multicolour, in particular full colour device). The patterned layer is typically a layer of photoresist that is patterned to define wells as described in, for example, EP 0880303.

As an alternative to wells, the ink may be printed into channels defined within a patterned layer. In particular, the photoresist may be patterned to form channels which, unlike wells, extend over a plurality of pixels and which may be closed or open at the channel ends.

Other solution deposition techniques include dip-coating, roll printing and screen printing.

If multiple layers of an OLED are formed by solution processing then the skilled person will be aware of techniques to prevent intermixing of adjacent layers, for example by crosslinking of one layer before deposition of a subsequent layer or selection of materials for adjacent layers such that the material from which the first of these layers is formed is not soluble in the solvent used to deposit the second layer.

EXAMPLES Monomer Example 1

Monomer Example 2

Synthesis of Monomer Example 3

Step 1: Synthesis of 4,6-Bis-(4-tert-butylphenyl)-[1,3,5]triazin-2-ol (3)

S. Quantity Vol. No Reagent (g) (mL) MW Moles Eq. 1 4-tert-Butylbenzonitrile (1) 60 159 0.377 1 2 Urea 5.66 60 0.094 0.25 3 NaH (60% in mineral oil) 9.04 24 0.188 0.5 4 DMSO 500

Apparatus Set-Up:

A 2 L 3-necked round-bottomed flask, equipped with a mechanical overhead stirrer, condenser, nitrogen inlet and exhaust.

Experimental Procedure

-   -   1) To a solution of 4-tert-butyl-benzonitrile (60 g, 0.377 mol),         urea (5.66 g, 0.094 mol) in DMSO (500 mL), sodium hydride (9.04         g, 0.188 mol) was slowly added in small portions at room         temperature and stirred for 16 h.     -   2) After completion of the reaction mixture, 5% acetic acid in         water (1 L) was added and stirred for an hour.     -   3) The white solid formed was filtered, washed with water (500         mL), petroleum ether (200 mL) and dried under vacuum to afford         4,6-Bis-(4-tert-butyl-phenyl)-[1,3,5]triazin-2-ol (3) (50 g,         73%) as white solid.     -   4) It was used without further purification in the next step.

Step 2: Synthesis of 2,4-Bis-(4-tert-butyl-phenyl)-6-chloro-[1,3,5]triazine (4)

S. Quantity Vol. No Reagent (g) (mL) MW Moles Eq. 1 4,6-Bis-(4-tert-butyl- 50 361.5 0.138 1 phenyl)-[1,3,5]triazin-2-ol 2 POCl₃ 500

Apparatus Set-Up:

A 1 L 3-necked round-bottomed flask, equipped with a mechanical overhead stirrer and condenser.

Experimental Procedure

-   -   1) A mixture of         4,6-Bis-(4-tert-butylphenyl)-[1,3,5]triazin-2-ol (2) (50 g,         0.138 mol) and POCl₃(500 mL) was heated at 90° C. for 3 h.     -   2) After completion of the reaction, POCl₃ was distilled off         under high vacuum.     -   3) The residue thus obtained was carefully added to ice cold         water (1000 mL) and stirred for 30 min.     -   4) The solid thus formed was filtered, washed with water, dried         under vacuum to afford         2,4-Bis-(4-tert-butyl-phenyl)-6-chloro-[1,3,5]triazine (4) as         white solid (25 g, 47%, 98.7% pure by HPLC).

¹H-NMR (400 MHz, CDCl₃): δ [ppm] 1.40 (s, 18H), 7.57 (d, J=6.4 Hz, 4H), 8.54 (d, J=6.4 Hz, 4H).

Step 3: Synthesis of 4-[4,6-Bis-(4-tert-butyl-phenyl)-[1,3,5]triazin-2-yl]-benzaldehyde (6)

S. Quantity Vol. No Reagent (g) (mL) MW Moles Eq. 1 2,4-Bis-(4-tert-butyl- 37 379.93 0.097 1 phenyl)-6-chloro- [1,3,5]triazine (4) 2 4-Formyl phenyl 21.89 149.94 0.1460 1.5 boronic acid (5) 3 PdCl₂(PPh₃)₂ 3.4 701.9 0.0048 0.05 4 Na₂CO₃ 37.1 106 0.350 3.6 5 Dioxane 500

Apparatus Set-Up:

A 3 L 3-necked round-bottomed flask, equipped with a mechanical overhead stirrer, condenser, nitrogen inlet and exhaust.

Experimental Procedure

-   -   1) To a solution of         2,4-Bis-(4-tert-butylphenyl)-6-chloro-[1,3,5]triazine (4) (37 g,         0.097 mol) in Dioxane (500 mL) and water (250 mL) mixture was         added 4-Formyl phenyl boronic acid (5) (21.89 g, 0.1460 mol).     -   2) The reaction mixture was degassed under N₂ for 30 min.     -   3) To the reaction mixture Na₂CO₃ (37.1 g, 0.350 mol) followed         by PdCl₂(PPh₃)₂ (3.4 g) was added and stirred.     -   4) The reaction mixture was heated at 100° C. for 16 h.     -   5) Reaction was monitored by TLC.     -   6) The reaction mixture was cooled to RT and passed through a         bed of celite.     -   7) The celite bed was washed with DCM (800 mL).     -   8) The organic layer was separated and washed with brine (100 mL         x 2).     -   9) The organic layer was dried over sodium sulphate and         concentrated under vacuum to afford         4-[4,6-Bis-(4-tert-butyl-phenyl)-[1,3,5]triazin-2-yl]-benzaldehyde (6)         (37 g, 84%, 98.8% pure by HPLC).

¹H-NMR (400 MHz, CDCl₃): δ [ppm] 1.42 (s, 18H), 7.62 (d, J=8.56 Hz, 4H), 8.09 (d, J=8.32 Hz, 2H), 8.69 (d, J=8.56 Hz, 4H), 8.93 (d, J=8.24 Hz, 2H), 10.17 (s, 1H).

Step 4: Synthesis of Wittig Salt 1

S. Quantity Vol. No Reagent (g) (mL) MW Moles Eq. 1 Intermediate 1 20 556.02 0.0359 1 2 Triphenylphosphine 28.37 263.02 0.107 3 3 Toluene 400

Apparatus Set-Up:

A 1 L 3-necked round-bottomed flask, equipped with a mechanical overhead stirrer, condenser, nitrogen inlet and exhaust.

-   -   1) To a solution of Intermediate 1 (20 g, 0.0359 mol) in Toluene         (800 mL), triphenylphosphine (28.37 g, 0.107 mol) was slowly         added in small portions at room temperature and heated to         100° C. for 16 h.     -   2) Reaction was monitored by TLC.     -   3) The reaction mixture was cooled to RT, vigorously stirred for         1 h.     -   4) Solid separated was filtered and given dry Diethyl ether         wash.     -   5) The residue thus obtained was dried under nitrogen atmosphere         to afford Wittig salt 1 (32 g, 75%) as a white solid. It was         used as such in next step.

Step 5: Synthesis of Intermediate 7

S. Quantity Vol. No Reagent (g) (mL) MW Moles Eq. 1 4-[4,6-Bis-(4-tert-butyl- 25 449.50 0.0556 1 phenyl)-[1,3,5]triazin-2- yl]-benzaldehyde (6) 2 Wittig Salt 1 32.8 1182 0.0278 0.5 3 Sodium tert-pentoxide 6.73 110.13 0.0611 1.1 4 Toluene 500

Apparatus Set-Up:

A 2 L 3-necked round-bottomed flask, equipped with a mechanical overhead stirrer, condenser, nitrogen inlet and exhaust.

Experimental Procedure

-   -   6) To a solution of         4-[4,6-Bis-(4-tert-butyl-phenyl)-[1,3,5]triazin-2-yl]-benzaldehyde         (25 g, 0.0556 mol), Wittig Salt 1 (32.8 g, 0.0278 mol) in         Toluene (800 mL), sodium tert-pentoxide (6.73 g, 0.0611 mol) was         slowly added in small portions at room temperature and heated to         110° C. for 16 h.     -   7) Reaction was monitored by TLC.     -   8) The reaction mixture was cooled to RT and passed through a         bed of celite and washed with DCM (700 mL)     -   9) The organic layer was washed with 5% aqueous HCl solution         (200 mL) and water (150 mL)     -   10) The combined organic layer was washed with brine (100 mL),         dried over sodium sulphate and concentrated to afford 7 as crude         compound (37 g).     -   11) The crude compound was purified by column chromatography         (silica gel, 230-400 mesh) using 10% DCM in hexane to afford (7)         (13 g, 18%, 89% pure by HPLC).

¹H-NMR (400 MHz, CDCl₃): δ [ppm] 1.42 (s, 36H), 1.55-1.60 (m, 12H), 2.43-2.46 (m, 4H), 2.65 (t, J=7.48 Hz, 4H), 5.78-5.81 (m, 2H), 6.54 (d, J=11.60, 2H), 7.35 (s, 2H), 7.48 (d, J=8.28 Hz, 4H), 7.61 (d, J=8.44 Hz, 8H), 8.69-8.76 (m, 12H)

Step 6: Synthesis of Monomer 1

S. Quantity Vol. No Reagent (g) (mL) MW mmoles Eq. 1 Intermediate 7 1 1267 0.789 1 2 PtO₂ 0.1 10% 3 THF 15 4 MeOH 5

Apparatus Set-Up:

A 100 mL Miniclave.

Experimental Procedure

-   -   1) A mixture of intermediate 7 (1 g, 0.789 mmol) and platinum         oxide (0.1 g) in

THF-methanol (3:1, 20 mL) was hydrogenated at room temperature for 2 h (H² 3 Kg/cm²).

-   -   2) Reaction was monitored by HPLC.     -   3) The catalyst was removed by celite filtration and the         filtrate was concentrated.     -   4) The crude residue was purified by column chromatography         (silica gel, 230-400 mesh) using 1% EtOAC in petroleum ether         followed by crystallization with acetonitrile twice yields (0.7         g, 70%) of Monomer 1 as a white solid, 93% pure by HPLC.

¹H-NMR (400 MHz, CDCl₃): δ [ppm] 1.40-1.46 (m, 12H), 1.45 (s, 36H), 1.57-1.64 (m, 4H), 1.68-1.72 (m, 4H), 2.66 (t, J=7.96 Hz, 4H), 2.74 (t, J=7.84 Hz, 4H), 7.37 (s, 2H), 7.39 (d, J=8.24 Hz, 4H), 7.61 (d, J=8.48 Hz, 8H), 8.68-8.72 (m, 12H).

Polymer Example 1

A polymer was prepared by Suzuki polymerisation as described in WO 00/53656 of Monomer Example 1 and a fluorene monomer suitable for forming a highly conjugated repeat unit of formula (IVa).

Modelling Results

The effect of substituents ortho- to a linking position and the effect of the linking position of an internally conjugated repeat unit was measured using a phenylene chain, as illustrated below, wherein R is alkyl:

n 1/n S1 T1 1 1 5.2286 3.4803 2 0.5 4.3873 3.1537 3 0.333333 4.0915 3.0546 0 3.5300 2.8372

n 1/n S1 T1 1 1 5.2177 3.6904 2 0.5 5.0403 3.6073 3 0.333333 4.9925 3.5866 0 4.8747 3.5315

n 1/n S1 T1 1 1 5.2286 3.4803 2 0.5 4.6507 3.2348 3 0.333333 4.5452 3.1809 0 4.1633 3.0183

n 1/n S1 T1 1 1 5.3077 3.6884 2 0.5 5.0259 3.5605 3 0.333333 4.9598 3.5272 0 4.7730 3.4423

Geometry optimization was performed by the Hartree-Fock method with the basis of 6-31 g*, then with the said optimized structure, TDDFT of B3P86 level with the same 6-31 g* basis was applied to calculate S₁ and T₁ energy. Gaussian03 was used for all calculations. The calculations were performed for 1, 2, and 3 repeat units [1 repeat unit=(A−B)] and extrapolated to (1/n)=0.

As can be seen the triplet level T₁ is increased for conjugation-reducing repeating units, and by at least 0.18 eV for a meta-linked phenyl group. For twisting units, the triplet level is increased by 0.69 eV.

Phenylene chains containing meta-linked repeat units and/or substitution ortho to a linking position have a higher energy triplet excited state (T₁) than an unsubstituted, para-linked phenylene chain. Singlet energy excited state (S₁) generally increases with increase in T₁, and so an increase in S₁ may be indicative of an increase in T₁.

Although a reduction in S₁ and T₁ levels is observed at higher values of n for chains including substituted and/or meta-linked phenyl, indicating some degree of conjugation in these chains, it will be appreciated that the S₁ and T₁ levels for these chains is higher than that of an unsubstituted, para-linked phenylene chain.

Device Examples

An organic light-emitting device having the following structure was prepared:

ITO/HIL/HTL/LE/Cathode

Wherein ITO is an indium-tin oxide anode; HIL is a hole-injecting layer comprising a hole-injecting material, HTL is a hole-transporting layer, LE is a light-emitting layer formed by spin-coating Polymer Example 1; and the cathode comprises a layer of metal fluoride in contact with the light-emitting layer and a layer of aluminium formed over the layer of metal fluoride.

General Device Fabrication Process

A substrate carrying ITO was cleaned using UV/Ozone. The hole injection layer was formed by spin-coating an aqueous formulation of a hole-injection material available from Plextronics, Inc. A hole transporting layer was formed to a thickness of 20 nm by spin-coating and crosslinked by heating. A light-emitting layer was formed by depositing a light-emitting formulation to a thickness of 75 nm by spin-coating from o-xylene solution. A cathode was formed by evaporation of a first layer of a metal fluoride to a thickness of about 2 nm, a second layer of aluminium to a thickness of about 200 nm and an optional third layer of silver.

Although the present invention has been described in terms of specific exemplary embodiments, it will be appreciated that various modifications, alterations and/or combinations of features disclosed herein will be apparent to those skilled in the art without departing from the scope of the invention as set forth in the following claims. 

1. A composition comprising a polymer and at least one phosphorescent light-emitting dopant wherein: the polymer comprises a polymer backbone and charge transporting groups pendant from the polymer backbone; the polymer backbone is partially conjugated; and the polymer has a triplet energy level of at least 2.4 eV.
 2. A composition according to claim 1 wherein the polymer backbone comprises one or more highly conjugating repeat units and one or more conjugation-reducing repeat units that increase the triplet energy level of the polymer as compared to a polymer containing the highly conjugating repeat units only.
 3. (canceled)
 4. A composition according to claim 2 wherein the one or more conjugation-reducing repeat units are selected from: (i) non-conjugating repeat units that break any conjugation path between repeat units adjacent to the non-conjugating repeat unit; and (ii) conjugation-limited repeat units having a substitution pattern and/or linkage to adjacent repeat units that limits the extent of conjugation of the repeat unit to adjacent repeat units.
 5. A composition according to claim 2 wherein one or more highly conjugating repeat units are not substituted at any position adjacent to linking positions linking the highly conjugating repeat unit to adjacent repeat units.
 6. A composition according to claim 4 wherein the polymer comprises at least one conjugation-limited repeat unit, and wherein the conjugation-limited repeat unit has at least one substituent at a position adjacent to at least one position linking the conjugation-limited repeat unit to adjacent repeat units.
 7. A composition according to claim 1 wherein the polymer comprises repeat units of formula (I):

wherein Ar⁶ represents an aryl or heteroaryl group that is unsubstituted or substituted with one or more substituents R¹ independently selected in each occurrence from the group consisting of optionally substituted alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, N, C═O and —COO—; optionally substituted aryl or heteroaryl, preferably aryl or heteroaryl optionally substituted with one or more alkyl groups, optionally C₁₋₂₀ alkyl; and optionally substituted arylalkyl or heteroarylalkyl, and w is at least
 1. 8-9. (canceled)
 10. A composition according to claim 7 wherein at least one substituent R¹ has formula -(Sp)_(n)-CT, wherein n is 0 or 1; Sp in each occurrence independently in each occurrence represents a spacer group; and CT represents the charge transporting group.
 11. A composition according to claim 10 wherein Sp comprises at least one atom between CT and Ar⁶ breaking any conjugation path between CT and Ar⁶. 12-13. (canceled)
 14. A composition according to claim 7 wherein the polymer comprises at least one highly conjugating repeat unit of formula (I) and at least one conjugation-limited repeat unit of formula (I).
 15. A composition according to claim 14 wherein the highly conjugating repeat unit of formula (I) is a 2,7-linked fluorene repeat unit of formula (IVa):

wherein R² in each occurrence is H or a substituent R¹ independently selected in each occurrence from the group consisting of optionally substituted alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, N, C═O and —COO—; optionally substituted aryl or heteroaryl, preferably aryl or heteroaryl optionally substituted with one or more alkyl groups, optionally C₁₋₂₀ alkyl; and optionally substituted arylalkyl or heteroarylalkyl, and the repeat unit of formula (IVa) is not substituted in a position ortho- to the 2- or 7-positions.
 16. (canceled)
 17. A composition according to claim 14 wherein the conjugation-limited repeat unit of formula (I) is a phenylene repeat unit of formula (Va):

wherein R¹ is a substituent independently selected in each occurrence from the group consisting of optionally substituted alkyl wherein one or more non-adjacent C atoms may be replaced with O, S, N, C═O and —COO—; optionally substituted aryl or heteroaryl, preferably aryl or heteroaryl optionally substituted with one or more alkyl groups, optionally C₁₋₂₀ alkyl; and optionally substituted arylalkyl or heteroarylalkyl; and p is at least
 1. 18. A composition according to claim 1 wherein the charge-transporting group is a hole transporting group.
 19. (canceled)
 20. A composition according to claim 1 wherein the charge-transporting group is an electron-transporting group.
 21. (canceled)
 22. A composition according to claim 1 wherein the polymer and the at least one light-emitting dopant are blended together.
 23. A composition according to claim 1 wherein the at least one light-emitting dopant is bound to the polymer.
 24. A composition according to any preceding claim wherein the at least one light-emitting dopant is a blue light-emitting dopant or a green light-emitting dopant. 25-27. (canceled)
 28. An organic light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and the cathode wherein the light-emitting layer comprises a composition according to claim
 1. 29-30. (canceled)
 31. A polymer comprising a repeat unit of formula (Vd), (Ve) or (Vf):

wherein R¹ in each occurrence is the same or different and represents a substituent; p is at least 1; and at least one group R¹ has formula -(Sp)_(n)-CT, wherein n is 0 or 1; Sp in each occurrence independently in each occurrence represents a spacer group; and CT represents a charge transporting group. 32-33. (canceled)
 34. A composition comprising a polymer according to claim 31 and a phosphorescent light-emitting dopant.
 35. An organic light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and the cathode wherein the light-emitting layer comprises a composition according to claim
 31. 